Increase in local cerebral blood flow induced by circulating adrenaline: involvement of blood‐brain barrier dysfunction

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Abstract
The influence of i.v. adrenaline infusion [epinephrine, E] (8 .mu.g kg-1 per min-1) on local cerebral blood flow (CBF) in paralyzed and artificially ventilated rats was measured autoradiographically with 14C-iodoantipyrine as the diffusible tracer. At this dose, E invariably increased local CBF even though blood pressure was close to normal at the time of the CBF measurement. On the average, local CBF increased to 400% of control. In 6 of 9 animals the increase in flow was inhomogenous with randomly distributed areas of very high flow rates. Experiments with i.v. administration of Evans blue prior to E infusion showed that areas of Evans blue extravasation appeared in 3 of 4 animals. Although areas of extravasation often corresponded to areas of high flow rates, the former were much more circumscribed. Very high flow rates were found in areas showing no sign of blood-brain barrier dysfunction. The increase in CBF apparently was at least partly due to a pressure-mediated passage of E across the blood-brain barrier, but such a passage can occur in the absence of macroscopically visible protein extravasation.